Method for depositing nickel- and chromium (VI) -free metal matte layers

ABSTRACT

A method for depositing metal matte layers free of nickel and chromium(VI).

FIELD OF THE INVENTION

The present invention relates generally to a method for depositing nickel- and chromium(VI)-free metal matte layers on substrates.

BACKGROUND OF THE INVENTION

Metal matte layers are used for functional or decorative surface refinement in various areas. Thus, for example, in the area of jewelry production, surfaces are coated with appropriate matte layers for aesthetic reasons. In the area of household appliances or food preparation apparatuses or facilities, surfaces are often equipped with matte layers for decorative reasons.

The matte layers previously known in the state of the art are deposited from nickel-containing electrolytes, mostly chromium(VI)-containing electrolytes, and form a cover layer containing nickel. Although chromium(VI) is not detectable in the end layer with a careful operation, in particular, when rinsing after chrome-plating, there is some concern about layers which have been deposited from such electrolytes.

Nickel can lead to allergenic reactions with intensive skin contact or with the intake of nickel traces via foods. In the case of jewelry, it is precisely close skin contact and the nickel desorption promoted by sweat and moisture which lead to strong skin irritations. In the case of household appliances and food preparation facilities or apparatuses, contacting food with matte surfaces may, under certain circumstances, lead to the dissolving out of nickel, since the chromium layer does not always sufficiently cover the underlying microstructural surface.

For the aforementioned reasons, great efforts are being made, especially in the jewelry industry and in the area of the production of household appliances and food preparation apparatuses or facilities, to avoid such surface coatings.

However, since matted surfaces have a great aesthetic effect, corresponding surfaces in the aforementioned areas are currently used widely in spite of their disadvantages.

Taking into consideration what has been said in the preceding, the problem addressed by this invention is the provision of a method for the deposition of matte nickel- and chromium(VI)-free metal layers.

SUMMARY OF THE INVENTION

Among the objects of the invention, therefore, is the provision of a method to deposit matte surface layer free of nickel and chromium(VI) on substrates.

Briefly, therefore, the invention is directed to a method for depositing a matte layer free of nickel and chromium(VI) onto a substrate. The method comprises coating the substrate with a first matte metal layer that is free of nickel; and metallizing the first matte metal layer with a second metal layer that is free of nickel and chromium(VI), which assumes the matte effect of the first matte metal layer. The first matte metal layer comprises at least one metal selected from the group consisting of copper, silver, tin, zinc, or an alloy that does not contain nickel. The second metal layer comprises at least one metal selected from the group consisting of copper, tin, zinc, chromium(III), silver, gold, ruthenium, platinum, palladium, or an alloy of these metals.

The invention is also directed to a method for imparting a decorative matte finish to a surface of an article comprising coating the surface with a first matte layer of metal which a) contains at least one metallic material selected from the group consisting of copper, tin, silver, zinc, and metal alloys, and b) is substantially nickel-free; and depositing a second matte layer over the first matte layer, which second matte layer is a layer of metal which a) contains at least one metallic material selected from the group consisting of copper, tin, zinc, chromium, silver, gold, ruthenium, platinum, palladium, and metal alloys of the foregoing, b) is substantially free of nickel, c) is deposited from a composition which is substantially free of chromium (VI), and d) has a matte appearance.

Other objects and features of this invention will be in part apparent and in part pointed out hereinafter.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This application claims priority from German application number 103 54 760.6, the entire disclosure of which is explicitly incorporated by reference.

In accordance with this invention, a method for the deposition of nickel- and chromium(VI)-free metal matte layers is provided, the method comprising the following steps:

-   -   a) coating a substrate with a first matte layer;     -   b) metallizing the first matte metal layer with a second metal         layer that assumes the matte effect of the first metal layer to         obtain a coated substrate with a matted surface. According to         the invention, the first matte metal layer is nickel-free and         the second metal layer is free from nickel and chromium(VI). The         metal used to produce the first matte metal layer comprises at         least one metal of the group consisting of copper, silver, tin,         zinc, or an alloy that does not contain nickel. The metal used         to produce the second metal layer comprises at least one metal         of the group consisting of copper, tin, zinc, chromium(III),         silver, gold, ruthenium, platinum, palladium, or an alloy of         these metals.

In the context of this invention, the term “matte” refers to a dull, non-glare, or pearl surface finish.

In one aspect, the use of matte copper layers as a first matte metal layer turns out to be particularly suitable with the method of the invention. Such copper layers are obtained with the method of galvanic or chemical metallization, known in the state of the art.

In another aspect according to the invention, a second metal layer assuming the matte effect of the first metal layer using copper-tin alloys, such as white bronzes, proves to be particularly favorable. Such second metal layers impart the aesthetic impression of chromed matte nickel layers, but exhibit no allergenic potential and have sufficient mechanical stability and corrosion resistance.

In another aspect of the invention, if the mechanical stability is to be increased for technical application reasons, the proposal is made to metallize a third metal layer onto the second metal layer, which assumes the matte effect of the first metal layer, the third layer having corresponding mechanical characteristics. Here, the deposition of a chromium or chromium alloy layer, such as chromium alloys comprising vanadium, molybdenum, carbon, phosphorous, or tungsten from chromium(III)-containing electrolytes have proved to be suitable. Likewise, hard layers applied by a CVD or PVD, such as chromium carbide, titanium nitride/carbide, zirconium nitride/carbide, silicon dioxide, or DLC (diamond-like carbon) or combinations of these layers, have also proved to be suitable.

In one embodiment, the thickness of each layer is at least about 3 μm, for example, each layer is between about 5 μm and about 30 μm thick. In one such embodiment, the layers are about 10 μm thick.

With regard to the first matte metal layer, in one exemplary embodiment, an electrolyte suitable for carrying out the method of the invention is prepared with an acidic matte copper electrolyte, which produces matte layers by employing additives. For example, one electrolyte comprises the additive Cuprostar LP1, which is an additive commercially available from Enthone Inc. Such an electrolyte is applied to a substrate by applying a current. Other examples for electrolytes which can be used in the method of the invention for the deposition of matte copper layers are currentless copper electrolytes, such as ENPLATE CU 872, commercially available from Enthone Inc.

With regard to the second metal layer, in one embodiment according to this invention, a first matte copper layer obtained by means of a copper electrolyte according to this invention can be metallized with a copper-tin alloy in the next method step. An advantageous electrolyte for the galvanic deposition of copper-tin alloys, such as white bronzes, comprises tin and copper ions in the form of cyanides, as well as suitable additives such as alkali liquor and free cyanide. Alkylsulfonic acid electrolytes comprising an aromatic, nonionic wetting agent can also be used. The electrolyte may optionally comprise additional stabilizers and/or anionic and/or nonionic complexing agents, aliphatic wetting agents, antioxidation agents, and other metal salts.

The metals tin and copper, which are introduced into the electrolytes mainly for the deposition of bronzes, can be present predominantly as cyanides. In the case of the acidic electrolytes, they can be present as salts of alkylsulfonic acids, preferably as methane sulfonates, or as salts of mineral acids, preferably as sulfates. In one preferred embodiment, the tin salt tin methane sulfonate is used in the electrolyte. It is advantageously added to the electrolyte in a quantity of about 5-195 g/L of electrolyte. This corresponds to a use of about 2-75 g/L divalent tin ions. In another preferred embodiment, possibly coupled with the preceding preferred embodiment, the copper salt copper methane sulfonate is used in the electrolyte. It is advantageously added to the electrolyte in a quantity of about 8-280 g/L. This corresponds to a use of about 2-70 g/L divalent copper ions.

Since the deposition rate in the acidic medium is clearly higher, an acid, preferably a mineral and/or an alkylsulfonic acid, is added to the electrolyte in quantities of about 140-382 g/L of electrolyte. The use of methanesulfonic acid is particularly advantageous, since it both causes an advantageous solubility of the metal salts and simultaneously, as a result of its acid strength, specifies or facilitates the setting of the pH value needed for the method. In addition, the methanesulfonic acid has the advantageous characteristic of substantially contributing to the stability of the bath.

In the following examples, which are given by way of illustration and are not limiting on the invention, electrolytes are described which are suitable for carrying out the method of the invention.

EXAMPLE 1

This is an acidic matte copper electrolyte, which can be used to produce the first matte metal layer by additives. An electrolyte was prepared comprising, by approximate composition:

-   -   18-25 g/L Cu²⁺     -   180-210 g/L H₂SO₄     -   30-80 mg/L Cl⁻     -   1-10 mL/L Cuprostar LP1

Cuprostar LP1 is an additive commercially available from Enthone Inc. The electrolyte was used to coat a substrate at a temperature range of between about 18° C. and 35° C. The electrolyte was used to coat a substrate by applying a current density between about 1 A/dm² and 5 A/dm².

EXAMPLES 2-5

For purposes of illustration, the following examples describe electrolytes suitable for use depositing the second metal layer.

EXAMPLE 2

An electrolyte was prepared comprising, by approximate composition:

-   -   5 g/L Sn²⁺     -   10 g/L Cu²⁺     -   240 g/L Methane sulfonic acid     -   32.2 g/L Aromatic, nonionic wetting agent     -   2 g/L Antioxidation agent     -   25 g/L Stabilizer/complexing agent

EXAMPLE 3

An electrolyte was prepared comprising, by approximate composition:

-   -   18 g/L Sn²⁺     -   2 g/L Cu²⁺     -   258 g/L Methane sulfonic acid     -   9 g/L Aromatic, nonionic wetting agent

EXAMPLE 4

An electrolyte was prepared comprising, by approximate composition:

-   -   17.0-25.0 g/L Sn²⁺     -   10.0-15.0 g/L Cu²⁺     -   1.3-1.9 g/L Zn²⁺     -   45.0-60.0 g/L KCN     -   0.5-2 mL/L Wetting agent     -   0.1-1 mL/L Gloss additive

The electrolyte of this example has a pH value of between about 12.4-12.9. It was applied to a substrate by applying a current density between about 2 and 4 A/dm² while holding the electrolyte in a temperature range between about 50° C. and about 60° C.

EXAMPLE 5

An electrolyte was prepared comprising, by approximate composition:

-   -   8.0-12.0 g/L Sn²⁺     -   5.0-10.0 g/L Cu²⁺     -   1.0-3.0 g/L Zn²     -   23.0-30.0 g/L KCN     -   0.1-2 mL/L ATC solution No. 4 from Enthone Inc.     -   0.1-2 mL/L BRONZEX WMF Brightener NG from Enthone Inc.

The electrolyte of this example has a pH value of between about 13.2-13.6. It was applied to a substrate by applying a current density between about 0.3 A/dm² and 0.7 A/dm² while holding the electrolyte in a temperature range between about 39.0° C. and 45.0° C.

When introducing elements of the present invention or the preferred embodiment(s) thereof, the articles “a,” “an,” “the,” and “said” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As various changes could be made in the above methods and products without departing from the scope of the invention, it is intended that all matter contained in the above description and shown in any accompanying drawings shall be interpreted as illustrative and not in a limiting sense. 

1. A method for depositing a matte layer free of nickel and chromium(VI) onto a substrate, the method comprising: (a) coating the substrate with a first matte metal layer that is free of nickel; (b) metallizing the first matte metal layer with a second metal layer that is free of nickel and chromium(VI), which assumes the matte effect of the first matte metal layer; wherein the first matte metal layer comprises at least one metal selected from the group consisting of copper, silver, tin, zinc, or an alloy that does not contain nickel; and wherein the second metal layer comprises at least one metal selected from the group consisting of copper, tin, zinc, chromium(III), silver, gold, ruthenium, platinum, palladium, or an alloy of these metals.
 2. The method of claim 1, wherein the first matte metal layer is deposited chemically.
 3. The method of claim 1, wherein the first matte metal layer is electrolytically deposited.
 4. The method of claim 1, wherein the second metal layer is chemically deposited.
 5. The method of claim 1, wherein the second metal layer is deposited electrolytically.
 6. The method of claim 1 further comprising coating the second metal layer with a third layer.
 7. The method of claim 6, wherein the third layer comprises chromium.
 8. The method of claim 6, wherein the third layer comprises chromium alloyed with at least one element selected from the group consisting of vanadium, molybdenum, carbon, phosphorous, tungsten, and mixtures thereof.
 9. The method of claim 1, the method further comprising coating the second metal layer with a third layer and at least one hard layer applied by CVD or PVD.
 10. The method of claim 9, wherein the hard layer comprises a material selected from the group consisting of chromium carbide, titanium nitride, titanium carbide, zirconium nitride, zirconium carbide, silicon dioxide, diamond-like carbon, and combinations thereof.
 11. The method of claim 9 wherein the third layer comprises chromium.
 12. The method of claim 9, wherein the third layer comprises chromium alloyed with at least one element selected from the group consisting of vanadium, molybdenum, carbon, phosphorous, tungsten, and mixtures thereof.
 13. A method for imparting a decorative matte finish to a surface of an article comprising: coating the surface with a first matte layer of metal which a) contains at least one metallic material selected from the group consisting of copper, tin, silver, zinc, and metal alloys, and b) is substantially nickel-free; and depositing a second matte layer over the first matte layer, which second matte layer is a layer of metal which a) contains at least one metallic material selected from the group consisting of copper, tin, zinc, chromium, silver, gold, ruthenium, platinum, palladium, and metal alloys of the foregoing, b) is substantially free of nickel, c) is deposited from a composition which is substantially free of chromium (VI), and d) has a matte appearance.
 14. The method of claim 13 further comprising depositing a third layer over the second metal layer, wherein the third layer comprises chromium, wherein the depositing the third layer is by a process employing a chromium-containing composition which is substantially free of chromium (VI).
 15. The method of claim 14, wherein the third layer comprises chromium alloyed with at least one element selected from the group consisting of vanadium, molybdenum, carbon, phosphorous, tungsten, and mixtures thereof.
 16. The method of claim 13 further comprising depositing a third layer over the second metal layer and a hard layer over the second metal layer by CVD or PVD.
 17. The method of claim 16, wherein the hard layer comprises a material selected from the group consisting of chromium carbide, titanium nitride, titanium carbide, zirconium nitride, zirconium carbide, silicon dioxide, diamond-like carbon, and combinations thereof.
 18. The method of claim 16 wherein the third layer comprises chromium.
 19. The method of claim 18, wherein the third layer comprises chromium alloyed with at least one element selected from the group consisting of vanadium, molybdenum, carbon, phosphorous, tungsten, and mixtures thereof.
 20. The method of claim 13 wherein the coating the surface with the first matte layer of metal comprises immersing the surface in an electrolyte comprising Cu ions and applying an external source of electrical current to the electrolyte to electrolytically deposit a Cu-based layer as the first matte layer.
 21. The method of claim 20 wherein the electrolyte comprises, by approximate composition: 18-25 g/L Cu²⁺ 180-210 g/L H₂SO₄ 30-80 mg/L Cl⁻.
 22. The method of claim 21 wherein the electrical current has a current density between about 1 A/dm² and 5 A/dm² and the electrolyte has a temperature in a range between about 18° C. and 35° C.
 23. The method of claim 13 wherein the second matte layer comprises tin and the depositing the second matte layer comprises immersing the surface in an electrolyte comprising Sn ions and applying an external source of electrical current to the electrolyte to electrolytically deposit a Sn-based layer as the second matte layer.
 24. The method of claim 23 wherein the second matte layer is deposited using an electrolyte comprising, by approximate composition: g/L Sn²⁺ 10 g/L Cu²⁺ 240 g/L methanesulfonic acid 32.2 g/L aromatic, nonionic wetting agent 2 g/L antioxidation agent 25 g/L stabilizer/complexing agent.
 25. The method of claim 23 wherein the second matte layer is deposited using an electrolyte comprising, by approximate composition: 18 g/L Sn²⁺ 2 g/L Cu²⁺ 258 g/L methanesulfonic acid 9 g/L aromatic, nonionic wetting agent.
 26. The method of claim 23 wherein the second matte layer is deposited using an electrolyte comprising, by approximate composition: 17.0-25.0 g/L Sn²⁺ 10.0-15.0 g/L Cu²⁺ 1.3-1.9 g/L Zn²⁺ 45.0-60.0 g/L KCN 0.5-2 mL/L wetting agent 0.1-1 mL/L gloss additive.
 27. The method of claim 26 wherein the electrolyte has a pH value of between about 12.4 and about 12.9.
 28. The method of claim 26 wherein the second matte layer is deposited at a temperature range of between about 50° C. and 60° C. and with a current density of between about 2 A/dm² and about 4 A/dm².
 29. The method of claim 13, wherein the second matte layer is deposited using an electrolyte comprising, by approximate composition: 8.0-12.0 g/L Sn²⁺ 5.0-10.0 g/L Cu²⁺ 1.0-3.0 g/L Zn² 23.0-30.0 g/L KCN
 30. The method of claim 29, wherein the electrolyte has a pH value of between about 13.2 and about 13.6.
 31. The method of claim 29, wherein the second matte layer is deposited at a temperature range of between about 39° C. and 45° C. and with a current density of between about 0.3 A/dm² and 0.7 A/dm².
 32. The method of claim 13, wherein the first matte metal layer comprises copper.
 33. The method of claim 13, wherein the second matte layer comprises tin and copper.
 34. The method of claim 13, wherein the second matte layer comprises tin, copper, and zinc.
 35. The method of claim 32, wherein the first matte metal layer is between about 5 μm and about 30 μm thick.
 36. The method of claim 35, wherein the second matte layer is between about 5 μm and about 30 μm thick.
 37. A method for imparting a decorative matte finish to a surface of an article comprising: immersing the surface in a first electrolyte comprising Cu ions and applying an external source of electrical current to the first electrolyte to electrolytically deposit a Cu-based layer as a first matte layer, wherein the first electrolyte is substantially nickel-free; and depositing a second matte layer over the first matte layer by immersing the surface in a second electrolyte comprising Sn ions and applying an external source of electrical current to the second electrolyte to electrolytically deposit a Sn-based layer as the second matte layer, wherein the second electrolyte is substantially free of nickel and is substantially free of chromium (VI). 